<!DOCTYPE html>
<html>

	<head>
		<meta charset="UTF-8">
		<title></title>
		<!--[if lt IE 9]>
    <script src="jquery-1.9.0.js"></script>
<![endif]-->
		<!--[if gte IE 9]><!-->
		<script src="../js/jquery-3.1.1.js"></script>
		<!--<![endif]-->
		<script type="text/javascript">
$(document).ready(function(){
  $(":selected").css("background-color","red");
});
		</script>
	</head>

	<body>
<form action="">
用户名: <input type="text" name="user"><br>
汽车品牌:
<select>
  <option>Volvo</option>
  <option selected="selected">Saab</option>
  <option>Mercedes</option>
  <option>Audi</option>
</select>
</form>
	</body>
</html>